Toupee, one adopted by Grace initially (3)
I believe the answer is:
wig
'toupee' is the definition.
(I've seen this in another clue)
'one adopted by grace initially' is the wordplay.
'one' becomes 'i' (Roman numeral).
'adopted by' means one lot of letters goes inside another (I've seen this in other clues).
'grace initially' becomes 'wg' (I am not sure about this - if you are sure you should believe this answer much more).
'i' going inside 'wg' is 'WIG'.
Can you help me to learn more?
(Other definitions for wig that I've seen before include "rug" , "carpet" , "Artificial head covering, toupee" , "Disguise for baldness" , "In America it's a toupee" .)